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' UNCLASSIFIED - 44 -TA r --·_ APAE-MEMO-29,

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* 'AUTHOR - R. D. ROBERTSON

-

CURRENT STATUS OF Afl'R-1 FUEL ELEMENT

METALLURGY

c photostat Price $. 3.30Microfilm Price $2• 4 0

/-

CONTRACT NO. AT(11=1)-318' Available from the. Office of Technical Services

Department of CommerceWashington 25, D. C.

ISSUED: JULY 230 1956

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CLASSIFICATION CANCELLEDli & li i //1D 28: F 882 DATE FEB 22 1957 441%

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For The Atomic Energy Commission:  .:  ': 1  6- (Ail

1-#,9, 244-U.il 3 :£ 27 9·=Im-t 

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4 R E 2· 0 8·3 E R: -1  3 i : r 41 fi i. I. f f  :5 wi# lei 1 i T : ALCO PRODUCTS, INC.

' 1 5 41 .I 5. a Z 1 li -9 JMPost Office Box 414

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DISCLAIMER

This report was prepared as an account of work sponsored by anagency of the United States Government. Neither the United StatesGovernment nor any agency Thereof, nor any of their employees,makes any warranty, express or implied, or assumes any legalliability or responsibility for the accuracy, completeness, orusefulness of any information, apparatus, product, or processdisclosed, or represents that its use would not infringe privatelyowned rights. Reference herein to any specific commercial product,process, or service by trade name, trademark, manufacturer, orotherwise does not necessarily constitute or imply its endorsement,recommendation, or favoring by the United States Government or anyagency thereof. The views and opinions of authors expressed hereindo not necessarily state or reflect those of the United StatesGovernment or any agency thereof.

DISCLAIMER

Portions of this document may be illegible inelectronic image products. Images are producedfrom the best available original document.

fee r. iFUEL ELEMENT METALLURGY

The devolopment by ORNL of fuel elements for the APER-1 has been

based on the use of 304L as the cladding material with highly enriched

uranium dioxide and a small quantity of boron carbide dispersed in a

sintered matrix of stainless steel as the fuel bearing coree The baron

carbide is introduced into the matrix as a burnable poison for controlling

excess reactivity at start-up.

Powder metallurgy techniques are used in preparing the coreo

The core is clad by the use of roll bonding and the picture frame technique.

Finished cladding thickness is .005"o and finished core thickness is 00201 o

A metallurgical bond is obtained between core and cladding and between

cladding elements themselvese

The materials used in the fuel bearing core of plates for both

stationary and control rod fuel elements are:

Stainless Steel Powder - type 304 with high silicon in a

size less than 149 mic,·onso

T02 POwder = highly enriched grade containing approximately

88% uranium in which the U-235 isotope is upgraded to product

levelo The oxide is prepared by the reduction of hydrated oxide=

uranyl nitrates commonly cmlled the Geneva process. Particle

size is 44-88 micronsp and the oxide powder is free of

elinging fineso

B4C Powder - contains approximately 76% natural boron and is

screened to less than 44 micron sizeo

176 002Id

..... .............. . . . .

...

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61/,/Rmirrint.

The st,dnless steel, uranium dioxide and boron carbide powder

for each batch are weighed separately before blendingo The oxide powder

is weighed inside a special box arrangement for handling enriched material.

The three materials are introduced into a glass container and blended in

an oblique blendero A small amount of lauryl alcohol is added near the

end of blending,

The blended powder is transferred to the die cavity in a box-type

enclosure on a hydraulic press. The powder is cold campacted under a

pressure of 33 tons per square inche

Ten compacts are loaded in a stainless steel sintering boat which

is then introduced into a high temperature furnace and sintered for one hour

at 21000 Fo A dry hydrogen atmosphere with a dew point of at least =700 F

ia Tnmintained during sinteringo At the conclusion of the sintering opera-

tion, the compacts are visually inspected and reloaded in the original dieand coined to correct for the shrinkage which · occurs during sinteringo

Acceptable compacts are weighed and stored in a desiccator for subsequent

useo

The cladding for the core is originally composed of three parts,

the frame for enclosing the four lateral edges Jf the zintered compact and

a top and bottom cover shield0 The frame piece is prepared by punching a

nearly square hole in plate material. The previously prepared core is

inserted in this hole in the frame and the cover pieces placed over and under

and welded to the frawe to form a three ply billeto

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The jacketed compact or billet is preheated before rolling to a

temperature of 21000 F for approximately 20 minutes in a muffle furnace

purged with hydrogeno The compacts are hot reduced on a 201' diameter and

301' face mi31 from 0390" to 00408 with a total reduction of approximately

90%0 The jacketed compacts are reheated for a minimum 0*,23minutes between

each pass xna after the final passo 'Hot reductions per pass are from 10

to 30%e Rolling direction is reversed after each passo After hot rolling

the scale is removed by pickling in an acid bath, and wire brushingo

The hot rolled plates are fluorcscoped to locate the outlines of

the core and the plate is marked for shearing. The fluoroscope examination

is also used as an inspection for gross segregation. The edges of the

composite plates are then trimmed to remove excess material and squared byshearingo

The plates are then cold rolled to a finished thickness of .030"°A 4 high mill with a 51' diameter work roll and 141' face is used. The re-

duction per pass is kept to less than 5% with total cold reduction approx-

imately 25%. The roll faces are lubricated with oil which is removed from

the finished plate by vapor degreasingo

The plates as cold rolled are wavy and archedo A flattening anneal

is required to bring the plates to acceptable flatnesso The plates are

batch stacked, pressure is applied between two bolt down platens with

aluinins being used to prevent sticking during annealingo Annealing is

done in an atmosphere of dry hydrogen at 2100' F for approximately two hours

followed by furnace cooling.

11 + , G 704-eviqi"*18'

-5-..... ..................

....... ... ............

-- -

. .The fuel plates are then refluoroscoped to locate the boundaries

of the core sectiono The core is positioned within dimensional limits speci-

fled in drawings D9=13=2007, D9=13-2006, A9=13-2010 and A9-13=20(1& 9 by means of

a template placed over the fuel plate. The outline of the finished fuel plate

ts marked for removal of excess inactive stainless steelo Finished specified

fuel plate size is obtained by shearing and batch machining to drawings I

89-13-20068 2007, A9=13-2010 and A943=2009. Machining lubricants are removed

by vapor degreasingo

Side plates with longltudinal grooves ninning the length of the plate  

are gang milled to drawings D9-13-20119 2014, to provide the recesses for the. side edges of the fuel plates. Combs are also machined, primarily for use as

supports for the ends of the assembled plates during the brazing operationo

The 18 fuel plates (16 in the ease of control rod elements), 2 side

plates and 2 combs are assembled for brazing. Coast Metals NP brazing alloy,

containing 50 Nip 27=Fe, 11-St, 8-Mo, 4=P nominally, is usedo A stainless

steel brazing jig supports the assembly in loading and brasing. A pair of side

plates and one end comb are initially positioned in the jigo The first fuel

plate is then introduced into positiono The jig is rotated in two directions

to 45' from the horizontal so that brazing alloy powder can be loaded in the

flat position and eemented with Nicro-braze eement. A special technique is

used to insure the location of the brazing alloy to prevent excessive spreading  

anto the fuel plate during brazingo This procedure ls repeated for each plate

Until All plates have been assembledo

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-dwill.ili;-The stainless steel brazing jig with the fuel element loaded is then

put into a muffle type brazing furnace. Helium is used as a purging gas at

low temperatures and pure dry hydrogen at high temperatureso Brazing tempera-ture is 2150* F and the unit is held at temperature for 5 minutes. Cooling

rate is governed by allowable distortion. Hydrogen is replaced by helium at a

temperature of approximately 1400' Fo

Fuel plate location and flatness are held to plus or minus 10% of

plate spacing except for the two outside plates. Tolerance on these plates as

measured down from side plate edges is plus or minus 5%.

End adapters are then welded to the ends of the stationary elements

after facing the endso The assembly is then machined to final dimensions per

drawing R943-1003. On the control rod fuel elements, a handle is welded to

the top end of the side plate before assembly and brazing. After brazing, a

pin is inserted through and welded to the handleso Assembly is per drawing

89=13-1004. The fuel element assembly is checked for squareness and lengthwisebowing by insertion in a box in which the inside dimensions are approximately

000310 amr the nominal fuel element external dimensionso

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fl.....8SPECIFICATIONS

Specifications for the manufacture of fuel elements and absorber

sections are being prepared in cooperation with Oak Ridge National Laboratory

personnel and are presently in final revisiono Fuel element loadings are as

follows:

Stationary Fuel Elements - per element

Fuel content - gro U-235 515o16+o38%

Enrichment = Product level lool%

Boron 10 - gro Oo483 +1075%

4.94%

Control Red Fuel Elements - per element

Fuel content - gre U-235 417*76+o38%eo59%

Enrichment i001%

Boron 10 = gro 00392 +1675%94094%

Tolerances are determined by aecuracies obtainable in analysiso weighing

and handlingo

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h.11'193111'91

FUEL ELEMENT IRRADIATION TESTS

Three test programs were undertaken to investigate the ability of

APPR-1 type fuel elements to perform satisfactorily.

One of these test4 described in detail in CF 5594-164 consisted of

exposure of encapsulated small sized specimens in the MTR. Test variations

in these samples included type of matrix material, type of oxide, initial oxide

particle size, oxide and poison contentsp burn=up and clad=core=clad proper=

tionso Examination of eight of these small sized samples has been made to date

by the Solid States Division of ORNLo Five of these samples received approxi-

mately 20% burn=up and the other three approximately 50% burn-upo On all

* eight samples no cracksp distortion, blistering, or other observable defects

were observedo

1.

Considerable effect of oxide particle size on hardness and ductility

of the stainless matrix material has been foundo On the 20% burn-up samples,

bend tests show fairly extensive core break=up in the oxide particle size range

of 7 to 11 microns. Minute core cracking was observed with oxide particle size

of 31 to 44 microns, 53 to 62 micron particles showed no evidence of cracking on

bendingo In general, samples containing oxide sizes under 31 microns showed

fairly extensive break-up while samples with larger particle size showed only

minute cracking in the range of 31 - 44 micronsp and no cracking with larger.

sizes. On the samples with 50% burn-upp there is not yet enough evidence to

establish a pattern. Complete evaluation must await examination of all -

irradiated sampleso

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00==IrHardness measurements also indicate the effect of oxide particle

size on hardness of matrix material under irradiationg as illustrated inthe following table:

HardnessOxide Particle Size VIIP = 2 KG Lead

(Microns) Before Irradiation 8fter Erradiation

7-11 204 475

31-44 184 42o

88 " 105 178 371

Although these results are not strictly conclusive because of the

limited number examined, the data indicates that particle sizes under 31 microns

have considerably more radiation-damage effect upon the matrix material thanlarger particle slzeso

Another irradiation testy described in detail in CF 55-6-39, consistedof exposure in the MTR 02 a full sized fuel elemenit adapted to MTR size require-ments. This full sized element received an estimated burn-up of 25 to 40%.Telescopic eicamination of the element as a unit, and of four plates removedfrom the elements showed.no defects except a possible crack in a small section

of a brazed jointo Metallurgical examination of the section containing this

questionable area revealed a surface irregularity rather than a cracko A

reddish-brown film ouilining the core section was evident cn all fuel plates.The third irradiation test, described in GF 5441-13 and CP 554-113,

was of a full sized element in the STR core at ARCOo However, this element hasreceived only a small portion of its proposed burn=up at the time of its removal

from the core some time agoo Corrosion resistance under STR operating conditions

 18'1m51Vr 1 --' 1''C CC9

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e.'1-ilizMhas been reported as excellento

In brief, all APPR-1 irradiation tests to date indicate that satis-

factory performance can be expected from APPR-1 fuel elements.

..

CONTROL RODS

It is presently planned to use Boron 10 as the absorber material in

the APPR control rods, dispersed in an iron matrix and clad with 304L stainless

steelo The method of fabrication is in general similar to that used in the

fabrication of the fuel bearing plates, with some variations due to the

difference in materials and end requirementso The picture frame technique is

again used as are powder metallurgy techniques for the preparation of the

Boron 10 and iron compacto Finished thiclcness of the absorber plate is .187"

' including 0032" claddingo Four plates are welded by the heliarc method into a

hollow box which is used in order to take advantage of the thermalizing effect

of the water in the center of the box on any fast neutrons which pass through

the sides of the box. Pertinent drawings are 89-13-2017 and 1002.

Absorber section loading is as follows:

Per element+

Boron 10 - gro 56o4 = 2% (tentative)

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tior:Immilum:'ll"/4ABSORBER IRRADIATION TESTS

The absorber plates were originally specified in ORNL-1613 as

dispersions of B  in a copper matrix ana clad with 304L stainless steelo

Development work at ORNL on absorber plates was continued on this ccmbina-

tion of materials. It soon became evident, however, that copper cored stain-

less clad plates could not be fabricated satisfactorily due to the differences

in properties of copper and stainless steel at hot rolling temperatures. A

wide range of temperatures was trieds but in all cases it appeared that copper

was flowing between the stainless ftame elements themselves, resulting in poorbondingo Welding of frame elements of the plates was considered, but wasrejected because it was doubtful that a good seal could be obtained

consistentlyo

A review of potential absorber and matrix materials was then instituted.

Other compounds of boron were unattractive because of the larger weight percent

amounts *hat would be required due to the smaller weight percent of boron in

these compoundso Stainless steel, nickel, and nickel alloys had to be eliminated

as matrix materials because of evidence of reaction with the boron compounds

occurring at hot rolling temperatures. Boron 10 appeared to be a desirable

absorbing element because of the much smaller amount of total poison required I

per absorber plateo At this timep however$ boron 10 was apparently in rather

short supply and obtainable from only one source. Further investigation revealed

that boron 10 in the quantities required for APPR-1 could be obtained from

ORNLo

Development work was therefore initiated on using boron 10 as the

absorber and iron powder as a matrix material. It was found that rolling could

1:2 0119.- ... ... ............

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-Ii/:.be performed in only one direction due to necessity for maintaining a square

and full thickness of core at the end adjacent to the fuel element. Also, since

starting thickness ef frame and covers is limited by ORNL press eapacityp

finished absorber plate thickness has been reduced to .187:' in order So obtain

the reduction desired for satisfactory bonding. This devel@pment work has

resulted in an absorber plate which is considered excellent from the structural

viewpointo

Considerable coneern, however, has developed as to the capability of I

beram=containing control rads to withstand irradiationo Under irradiation boron

is transibmmed into Lithium 7 and hellumo Calculations by ORNL personnel indicate

that the helium pressure resulting from bcron burn-up gould be·excessive pro=

vided the helium atoms formed diffused into a vcido Unfortunately, there is no

irradiation experience direetly comparable to the boron 10 dlsperston in aniron matrix proposed for the AI Pit=lo Wrought stainless steels containing boron

in amounts less than that required for APPR-1 absorber plates beeame tremendously  

embrittled under irradiationo Blisters or warts have developed #m an wmelad

irradiated 1% boron dispersion in titaniume Cracks have developed under trradia=

tien in an unclad dispersion of boron in zirconiumo Howeverp due to differences

in properties of materials, and of the finished plates, there.is a very good

possibility that the boron 10 dispersions in irma clad with .032¤ of stainless

steel will not develop irregularities or defgats which would bar them from giving

satisfactory serviceo The clearance between the control red housing and the

absorber box section is sufficiently large that a gross dist6rtion or a gross

surface blistering would be necessary to cause interferenee with the proper

funetirning of the control rod assemb»o

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Im order to attain irradiation damage experience as soon as possibleD

a program has been set up to make and irradiate small samples of boran dispersed

in iron and clad.with stainless steel. These. small samples will be inserted

in leaky rabbits and irradiated in the MTR in a manner similar to the Phase XI

APER-1 fuel element samplese The proposed test samples and irradiation cycles

are listed in the table below4

Tee Emijazg/1 ErloriSE

B Design Loading 1 110 2 S3 34 45. 5

. 460% Bgo Dasign loading 3 6

5 7

12% 810 D"ign Loading 3 85 9

Low Deasification Core * 3 10

High m . 0 3 11

Low m " * 5 12High n w 0 5 ·3 3

*These samples have subsequently been eliminated from the test.programo

This test is based upon the assumption that five MTR cycles are the

equivalmnt of 100% burn=up and that five.cycles will require appradmately 15

weeks irradiation. The 60% B content samples are included because preliminary10

calculations indicate that this content will furnish the required blackness at

the end of one eore lifee Xt isp of coursep necessary to check this content in

a....."Up1 K, C 013

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./0."=the APPR-1 low power tests at Schenectady. The sample containing 20% excess

B is included as a possible accelerated teste The low and high densificatian10

samples are included to determine the effects of processing variableso

These thirteen samples are presently being fabricated and it is ex=

peeted that they will be shipped to the MTR by June lsto Xt is also planned

to test a full size control rod adapted for insertion in the MTRo This full

sized element ls in the stage of prellminary design at the present timeD and itis expected that it will be fabricated and shipped to the MTR in ally.

. Xh the event that these tests prove 40 to be an unS esirable absorber

material, consideration has been given to other materials for both immediate

and long range baek-up effetso Calculations have been made by Alco which

indicate that Hafnium would be a satisfactory substitute absorber materiale

I*

A hollow box constructed of solid Hafnium with walls .3" «i .4' thick is required.

'. 1The awmilability of Hafnium for this purpose is being investigated by ARBo0

Practically all potential absorber materials have been considered by

Alco personnel and evaluated.in connection with the long range back«up efforbo

High cross section rare earth materials appear unsatisfactory with present fab=

rication teclmiques because of the large,amount of eaeh material that would be

required to attal[n readivity control throughout core life equivalent to the

present design using 8100 St is entirely possible, of course, that a new fabrics=

tien teelmique can be developed which would permit the inearporation of the

relatively large amount of materials neededo Cadmium, Possibly in the form of

a eadmilm silver alloy at a content of about 30%, appears to be a more likelylong range back=up material at this timeo Wall thicknesses again in the crdew

'. pill/'/mil9 H' ir.2. 6 014

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  of .041, would be requ:isedo An experimenfnl reactivity evaluation of any alternate

absorber material in the APPR-1 core is required before a final decision can be

made to use a material other than borono

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